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An optical frequency domain reflectometry (OFDR) shape sensor was demonstrated based on a femtosecond-laser-inscribed weak fiber Bragg grating (WFBG) array in a multicore fiber (MCF). A WFBG array consisting of 60 identical WFBGs was successfully inscribed in each core along a 60â cm long MCF using the femtosecond-laser point-by-point technology, where the length and space of each WFBG were 2 and 8â mm, respectively. The strain distribution of each core in two-dimensional (2D) and three-dimensional (3D) shape sensing was successfully demodulated using the traditional cross correlation algorithm, attributed to the accurate localization of each WFBG. The minimum reconstruction error per unit length of the 2D and 3D shape sensors has been improved to 1.08% and 1.07%, respectively, using the apparent curvature vector method based on the Bishop frame.
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This publisher's note contains a correction to Opt. Lett.48, 3219 (2023)10.1364/OL.486644.
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Limited by the multiplexing number of fiber Bragg grating (FBG), further improvement in the length of 3D shape sensing based on FBG technology is challenging. In this Letter, a wavelength-division and space-division multiplexing multicore fiber grating method is proposed, which extends the sensing length. Employing the femtosecond-laser point-by-point technology, we inscribed WDM grating arrays in six outer cores of a seven-core fiber, respectively. Three cores were utilized as a segment for shape sensing, and two such segments were offset by a specific length and combined to form a shape sensor. Utilizing an FBG interrogator, the proposed shape sensor achieved 2D and 3D shape sensing at a length of 967â mm and effectively mitigated the effects of temperature variations. In experiments, maximum shape reconstruction errors per unit lengths are 1.89%, 2.72%, and 1.47% for 2D shape, 3D shape, and an arbitrary shape under variable temperature conditions, respectively. The proposed method holds promise for further extending the shape sensing length by utilizing multicore fibers or fiber clusters containing more cores.
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We demonstrated a long-range and centimeter-spatial-resolution optical frequency domain reflectometry (OFDR) system based on an ultra-linear broadband optical frequency sweep. The high nonlinear sweeping effect of the distributed feedback (DFB) diode laser was suppressed by a pre-distortion method, ensuring that the injection-locking process remained stable during fast tuning over a large span. An optical linear frequency sweep (LFS) with a sweep range and sweep rate of up to 60â GHz and 15 THz/s, respectively, was ultimately obtained by optimizing the injection-locking system. The high performance OFDR based on the proposed LFS achieved a sampling spatial resolution of 1.71 mm. Furthermore, distributed strain sensing was implemented with high-spatial resolutions of about 5â cm and 7â cm in the measurement range over 1â km and 2â km, respectively.
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An optical fiber φ-OFDR shape sensor with a submillimeter spatial resolution of 200â µm was demonstrated by using femtosecond-laser-induced permanent scatter array (PS array) multicore fiber (MCF). A PS array was successfully inscribed in each slightly twisted core of the 400-mm-long MCF. The two-dimensional (2D) and three-dimensional (3D) shapes of the PS-array-inscribed MCF were successfully reconstructed by using PS-assisted φ-OFDR, vector projections, and the Bishop frame based on the PS-array-inscribed MCF. The minimum reconstruction error per unit length of the 2D and 3D shape sensor was 2.21% and 1.45%, respectively.
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A wide-range OFDR strain sensor was demonstrated based on femtosecond-laser-inscribed weak fiber Bragg grating (WFBG) array in standard SMF. A WFBG array consisting of 110 identical WFBGs was successfully fabricated along a 56â cm-long SMF. Compared with SMF, the cross-correlation coefficient of WFBG array was improved to 0.9 under the strain of 10,000⠵ε. The position deviation under the strain of 10,000⠵ε, i.e., 2.5 mm, could be accurately obtained and compensated simply by using peak finding algorithm. The maximum measurable strain of single- and multi-point strain sensing was up to 10,000⠵ε without using any additional algorithms, where the sensing spatial resolution was 5 mm.
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A distributed optical fiber refractive index sensor based on etched Ge-doped SMF in optical frequency domain reflection (OFDR) was proposed and demonstrated. The etched Ge-doped SMF was obtained by only using wet-etching, i.e., hydrofluoric acid solution. The distributed refractive index sensing is achieved by measuring the spectral shift of the local RBS spectra using OFDR. The sensing length of 10 cm and the spatial resolution of 5.25 mm are achieved in the experiment. The refractive index sensing range is as wide as 1.33-1.44 refractive index units (RIU), where the average sensitivity was about 757 GHz/RIU. Moreover, the maximum sensitivity of 2396.9 GHZ/RIU is obtained between 1.43 and 1.44 RIU.
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A φ-optical frequency domain reflectometry (OFDR) strain sensor with a submillimeter-spatial-resolution of 233â µm is demonstrated by using femtosecond laser induced permanent scatters (PSs) in a standard single-mode fiber (SMF). The PSs-inscribed SMF, i.e., strain sensor, with an interval of 233â µm exhibited a Rayleigh backscattering intensity (RBS) enhancement of 26â dB and insertion loss of 0.6â dB. A novel, to the best of our knowledge, method, i.e., PSs-assisted φ-OFDR, was proposed to demodulate the strain distribution based on the extracted phase difference of P- and S-polarized RBS signal. The maximum measurable strain was up to 1400 µÎµ at a spatial resolution of 233â µm.
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Distributed temperature sensing up to 600°C at a fiber length of 100.75 m based on optical frequency domain reflectometry (OFDR) was demonstrated using a standard single-mode fiber (SMF) without any treatment. The spatial resolution was 2.5â mm. An algorithm, instantaneous optical frequency resampling (IOFR), to eliminate the nonlinearity of the laser source was proposed and used to obtain calibrated reference and measurement signals that were used for temperature demodulation. Moreover, the temperature response stability of the annealed SMF was better than that of un-annealed SMF, where the temperature sensitivity was 1.96â GHz/°C at 600°C.
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We demonstrate for the first time, to the best of our knowledge, the fabrication of a high-quality fiber Bragg grating (FBG) in ZBLAN fiber by using an efficient femtosecond laser point-by-point technology. Two types of FBG, e.g., high coupling coefficient and narrow bandwidth grating, are successfully obtained. The coupling coefficient is strongly dependent on the grating order and pulse energy. A second-order FBG with an ultrahigh coupling coefficient of 325â m-1 and reflectivity of 97.8% is inscribed in the ZBLAN fiber. A pair of FBGs with a narrow FWHM of 0.30 and 0.09â nm are also demonstrated.
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A nondestructive measurement method based on an Optical frequency domain reflectometry (OFDR) was demonstrated to achieve Young's modulus of an optical fiber. Such a method can be used to measure, not only the averaged Young's modulus within the measured fiber length, but also Young's modulus distribution along the optical fiber axis. Moreover, the standard deviation of the measured Young's modulus is calculated to analyze the measurement error. Young's modulus distribution of the coated and uncoated single mode fiber (SMF) samples was successfully measured along the optical fiber axis. The average Young's modulus of the coated and uncoated SMF samples was 13.75 ± 0.14, and 71.63 ± 0.43 Gpa, respectively, within the measured fiber length of 500 mm. The measured Young's modulus distribution along the optical fiber axis could be used to analyze the damage degree of the fiber, which is very useful to nondestructively estimate the service life of optical fiber sensors immersed into smart engineer structures.
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OBJECTIVE: To study anterior nasal spine fractures, including the incidence, missed diagnosis rates, and relationship with shapes using computed tomography (CT). METHODS: Two hundred cases of axial CT images performed for maxillofacial trauma were reviewed. The incidence, correct, and missed diagnosis rates of anterior nasal spine fractures were studied. The relationship between the fracture and the shape of the anterior nasal spine was also analyzed. RESULTS: The rate of anterior nasal spine fractures was 22.00% (44 of 200). The diagnostic accuracy was 4.55% (2 of 44) and the missed diagnosis rate was 95.45% (42 of 44). The fracture rates of the double rod, single rod, triangle, and irregular anterior nasal spine were 33.85% (22 of 65), 32.26% (10 of 31), 12.24% (12 of 98), and 0.00% (0 of 6), respectively. The double and single rod types of anterior nasal spine were most likely to be fractured than the type of triangle (χ2 = 11.05, 6.67, P < .0167). No fracture was found in the irregular type of anterior nasal spine. CONCLUSION: Anterior nasal spine fractures are not rare and the high missed diagnostic rate results from unfamiliarity with the structure. Double and single rod types of anterior nasal spines are easy to fracture. Bony reconstruction and thin thickness of CT images are necessary for diagnosis.
Asunto(s)
Fracturas Maxilares/diagnóstico por imagen , Nariz/diagnóstico por imagen , Nariz/lesiones , Tomografía Computarizada por Rayos X , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Niño , Preescolar , Femenino , Humanos , Procesamiento de Imagen Asistido por Computador , Incidencia , Masculino , Maxilar/anatomía & histología , Maxilar/diagnóstico por imagen , Fracturas Maxilares/epidemiología , Fracturas Maxilares/etiología , Persona de Mediana Edad , Diagnóstico Erróneo , Nariz/anatomía & histología , Adulto JovenRESUMEN
Two types of series-integrated fiber Bragg gratings (SI-FBGs), i.e., strong and weak SI-FBGs, were inscribed in a standard single-mode fiber (SMF) using the femtosecond laser point-by-point technology. In the SI-FBGs inscribing system, the grating pitch of each FBG and the distance between the two adjacent FBGs in the SI-FBGs can be flexibly controlled by adjusting the inscription parameters. The strong SI-FBGs with different grating pitches and the weak SI-FBGs with an identical grating pitch were employed to successfully measure the temperature distribution in a tube furnace and the strain distribution on a cantilever beam, respectively. A high spatial resolution of less than 1 mm was achieved during the distributed temperature sensing experiment. Moreover, the spatial resolution could be improved by decreasing the distance between the two adjacent FBGs, i.e., decreasing the FBG length and the space between the two adjacent FBGs. Hence, the inscribed high-quality SI-FBGs have great potential to be developed as various quasi-distributed sensors with a high spatial resolution.